Various kinds of so-called "fixed volume" discharge devices have been previously described in the art - see for example U.S. Pat. No. 4,151,934, U.S. Pat. No. 4,170,318 which describe devices adapted for mounting on the neck of a container, and EP-A-0194407 which describes a measuring cup which, in use, is mounted inside an opening of a container. However, the devices which are described in the art are structurally and operationally complex, expensive to produce, give variable discharge volume and are difficult to modify to meet differing discharge requirements.